304TP / 316TP Seamless Stainless Steel Coil Tube for Economizer & Low-Pressure Heater
Manufacturer: Wenzhou Jixing Metal Materials Co., Ltd
Product Overview
This premium-grade stainless steel coil tube is purpose-engineered for economizer and low-pressure heater service in coal-fired power generation systems. Operating within a feedwater temperature range of 150–300 °C, the tube is specifically formulated to withstand the demanding thermal-hydraulic conditions of subcritical and supercritical boiler circuits. A critical design consideration in this service is the rigorous control of dissolved oxygen content in the feedwater, as even trace oxygen ingress can precipitate localized corrosion and drastically reduce service life. Wenzhou Jixing Metal Materials delivers seamless coil tubing that meets the exacting metallurgical and dimensional requirements of leading power plant OEMs worldwide.
Material & Properties
The product is available in two primary austenitic stainless steel grades, both manufactured to the TP (Tube, Seamless) specification:
- 304TP (UNS S30400): Contains a minimum of 18% chromium and 8% nickel, providing excellent general corrosion resistance in oxidizing feedwater environments. Ideal for economizer sections where thermal cycling is moderate and dissolved oxygen is well-controlled below 7 ppb.
- 316TP (UNS S31600): Adds 2–3% molybdenum to the 304 alloy matrix, significantly enhancing resistance to Flow Accelerated Corrosion (FAC), chloride-induced pitting, and intergranular corrosion. Recommended for low-pressure heater tubes operating at the upper end of the temperature range (250–300 °C) or in systems with elevated flow velocities exceeding 2.5 m/s.
Key Metallurgical Characteristics
- High-temperature oxidation resistance up to 870 °C (304TP) and 925 °C (316TP)
- Non-magnetic in the annealed condition
- Excellent weldability and formability for field spool fabrication
- Low thermal conductivity, reducing radiant heat losses in economizer banks
- Outstanding resistance to thermal shock and repeated heat cycling
Specifications
| Parameter | Specification |
|---|---|
| Material Grades | 304TP / 316TP (ASTM A213 / ASME SA-213) |
| Tube Form | Seamless coil (helical coil, single or double pass) |
| Outer Diameter (OD) | 19.05 mm – 76.2 mm (¾" – 3") |
| Wall Thickness | 1.65 mm – 6.35 mm (0.065" – 0.250") |
| Coil Mean Diameter | Custom (typically 1,200 – 3,000 mm) |
| Operating Temperature | 150 °C – 300 °C (feedwater) |
| Operating Pressure | Up to 25 MPa (depending on OD/WT) |
| Dissolved Oxygen Limit | ≤ 7 ppb (per NACE / EPRI guidelines) |
| Surface Finish | Mill finish / Pickled & Passivated (P&P) |
| End Condition | Plain ends, beveled, or prepared for socket weld / butt weld |
| Standards Compliance | ASTM A213, ASME SA-213, EN 10216-5, ISO 3506 |
Manufacturing Process
Wenzhou Jixing Metal Materials employs a fully integrated, quality-controlled manufacturing sequence to produce coil tubing of the highest integrity:
- Raw Material Selection: Vacuum-arc remelted (VAR) or electro-slag remelted (ESR) billets with certified low sulfur, phosphorus, and interstitial carbon content to minimize FAC susceptibility.
- Hot Piercing & Rolling: Billets are heated to 1,200–1,300 °C and hot-pierced to form seamless blanks, then hot-rolled to near-final dimensions on a planetary mill.
- Cold Drawing / Mandrel Drawing: Tubes are cold-worked to precise OD and wall thickness tolerances (±0.05 mm), achieving superior dimensional accuracy and improved fatigue strength.
- Solution Annealing: Full solution treatment at 1,050–1,100 °C followed by rapid water quench to restore full austenitic microstructure and maximum corrosion resistance.
- Pickling & Passivation: Immersion in controlled nitric/citric acid bath to remove scale and form a protective chromium oxide passive layer, verified by blue-dye or ferrous ion spot testing.
- Coiling / Spiraling: Tubes are cold-coiled to specified mean diameter and pitch using CNC-controlled coiling equipment, ensuring uniform curvature without work hardening or micro-cracking.
- Final Inspection: Each coil undergoes 100% hydrostatic pressure testing, eddy-current or ultrasonic flaw detection, and dimensional verification per ASTM A213 requirements.
Applications
Primary Service: Coal-Fired Power Plants (Fire Power Generation)
- Economizer Tubes: The coil tube absorbs waste heat from flue gases to preheat boiler feedwater from 150–250 °C, improving overall plant thermal efficiency by 2–4 percentage points. The austenitic stainless steel matrix provides long-term resistance to sulfuric acid dew-point corrosion at the cold end of the economizer.
- Low-Pressure Heater (LP Heater) Tubes: In the feedwater heating train, these coils serve as the tube bundle for surface condensers and LP feedwater heaters operating at 200–300 °C. The 316TP grade is particularly advantageous here due to its superior resistance to Flow Accelerated Corrosion (FAC) caused by high-velocity water flow across tube surfaces.
- Deaerator Bypass Lines: Where feedwater bypasses the deaerator under emergency conditions, the coil tube maintains integrity despite transient oxygen spikes.
- Boiler Feedwater Piping Loops: Custom-coiled configurations reduce the number of butt welds, minimizing potential leak paths in high-temperature feedwater circuits.
Secondary Applications
- Supercritical and ultra-supercritical (USC) boiler feedwater systems
- Combined cycle power plant feedwater heaters
- Industrial waste heat recovery units
Flow Accelerated Corrosion (FAC) Mitigation
Engineering Note: Flow Accelerated Corrosion remains the single most significant degradation mechanism in stainless steel economizer and LP heater tubing. FAC occurs when high-velocity water flow removes the protective chromium oxide film faster than it can repassivate. Wenzhou Jixing addresses this challenge through:
- Selection of 316TP grade with molybdenum enhancement for critical high-flow zones
- Strict control of interstitial carbon (≤ 0.03%) and sulfur (≤ 0.015%) in the base alloy
- Optimized coil geometry to minimize flow-induced turbulence and impingement attack
- Recommended surface roughness (Ra) ≤ 0.4 μm after passivation to promote uniform passive film formation
Quality Certifications & Compliance
- ISO 9001:2015 — Quality Management System certified
- ISO 14001 — Environmental Management System
- EN 10204 3.1 — Third-party material test certificates for every heat
- ASTM A213 / ASME SA-213 — Product conformity testing
- Hydrostatic Testing: 100% of coils tested at 1.5× maximum working pressure per ASTM A530
- Non-Destructive Testing: Eddy current or ultrasonic inspection for full-length flaw detection
- Chemical Analysis: Spectrometric verification of Cr, Ni, Mo, C, S, P for each heat number
- Traceability: Full heat-to-coil traceability documentation provided with each shipment
Unique Selling Points
- Specialized Power Plant Expertise: Decades of manufacturing experience dedicated to economizer and LP heater coil tubing for coal-fired power generation, with deep understanding of FAC mechanisms and oxygen control requirements.
- Dual-Grade Availability: Both 304TP and 316TP grades from a single source, enabling customers to optimize material selection by zone within the same heat exchanger design.
- FAC-Resistant Metallurgy: ESR/VAR remelted stock with tightly controlled chemistry specifically formulated to resist the aggressive flow-accelerated corrosion environment of 150–300 °C feedwater circuits.
- Custom Coil Configuration: Flexible manufacturing capability to produce coils to customer-specified mean diameter, pitch, and end preparation, reducing field fabrication time and weld count.
- Full Traceability & Third-Party Inspection: Complete documentation chain from raw material heat number to finished coil, supporting OEM audit requirements and power plant startup verification.
Technical Support & Customization
Wenzhou Jixing Metal Materials Co., Ltd offers comprehensive engineering support for coil tube selection, including:
- Material selection guidance based on feedwater chemistry (oxygen content, pH, conductivity, chloride level)
- Thermal-hydraulic performance modeling for economizer and LP heater coil configurations
- FAC risk assessment and mitigation recommendations for existing plant retrofits
- Custom coil geometry design to match OEM heat exchanger shell dimensions
- On-site inspection coordination with TPI agencies (BV, SGS, Lloyd's Register, DNV)
For detailed quotations, material certifications, or technical consultation, contact Wenzhou Jixing Metal Materials Co., Ltd directly to discuss your specific application requirements.